Soft shell crawfish, a seafood delicacy, has a potential market for growth in the aquaculture industry. Since the industry's collapse in the 1990's, the advent of new technologies like eyestalk ablation, automated hydraulic separation and distributed airlift systems has elevated the hope for restoration. In a distributed airlift system, airlifts and distribution pipes supply water to holding trays.
Airlifts are simple devices used to pump water by injecting air at the bottom of an open pipe. The combination of airlifts and distribution pipes has potential economic benefits for low head applications in recirculating aquaculture systems. This thesis focuses on guidelines for the design of individual airlifts highlighting the rules for deciding the sizing of the riser, gas to liquid ratio (G/L ratio) and the lift. It also explains the guidelines to be used for sizing of the tapered water distribution pipes in distributed airlift systems.
Airlift diameter selection was based on a water flow rate of 15 gpm to each tray. Experiments conducted on 2 and 3 pipes indicated that the 2 pipe supplies 15 gpm at an optimum G/L between 1 and 2 while using lesser air than a 3 pipe for a lift height of 12. The airlifts should be designed for 20% lift and with no airlift exceeding 25% lift. They should be operated with a G/L ratio between 1 and 2 to achieve an optimum rate of water flow and minimum energy consumption.
Distribution pipes should be designed to minimize head loss and prevent settling. The sizing of the water distribution pipes should be velocity based with a velocity in the distribution system between 1 and 3 fps. Tapering of distribution pipe is necessary to maintain the minimum velocity. This also reduces head loss along the length of the pipe. Table 4.9 in this thesis gives tapering requirements for soft shell crawfish systems with 5, 10, 15 and 20 trays in each row.